arXiv subjects

Olga Soloveva

Publications and source records attributed to Olga Soloveva.

23 records · Page 2Linked to original sources

arXiv2021

QCD at finite chemical potential in and out-of equilibrium

We review the transport properties of the strongly interacting quark-gluon plasma (QGP) created in heavy-ion collisions at ultrarelativistic energies, i.e. out-of equilibrium, and compare them to the equilibrium properties. The description of the strongly interacting (non-perturbative) QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. We study the transport coefficients such as the ratio of shear viscosity and bulk viscosity over entropy density, diffusion coefficients, electric conductivity etc. versus temperature and baryon chemical potential. Based on a microscopic transport description of heavy-ion collisions we, furthermore, discuss which observables are sensitive to the QGP formation and its properties.

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arXiv2021

Shear viscosity and electric conductivity of a hot and dense QGP with a chiral phase transition

We calculate two transport coefficients -- the shear viscosity over entropy ratio $η/s$ and the ratio of the electric conductivity to the temperature $σ_0/T$ -- of strongly interacting quark matter within the extended $N_f=3$ Polyakov Nambu-Jona-Lasinio (PNJL) model along the crossover transition line for moderate values of baryon chemical potential $0 \leq μ_B \leq 0.9$ GeV as well as in the vicinity of the critical endpoint (CEP) and at large baryon chemical potential $μ_B=1.2$ GeV, where the first-order phase transition takes place. The evaluation of the transport coefficients is performed on the basis of the effective Boltzmann equation in the relaxation time approximation. We employ two different methods for the calculation of the quark relaxation times: i) using the averaged transition rate defined via thermal averaged quark-quark and quark-antiquark PNJL cross sections and ii) using the 'weighted' thermal averaged quark-quark and quark-antiquark PNJL cross sections. The $η/s$ and $σ_0/T$ transport coefficients have a similar temperature and chemical potential behavior when approaching the chiral phase transition for the both methods for the quark relaxation time, however, the differences grow with increasing temperature. We demonstrate the effect of the first-order phase transition and of the CEP on the transport coefficients in the deconfined QCD medium.

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arXiv2021

Diffusion coefficient matrix of the strongly interacting quark-gluon plasma

We study the diffusion properties of the strongly interacting quark-gluon plasma (sQGP) and evaluate the diffusion coefficient matrix for the baryon ($B$), strange ($S$) and electric ($Q$) charges - $κ_{qq'}$ ($q,q' = B, S, Q$) and show their dependence on temperature $T$ and baryon chemical potential $μ_B$. The non-perturbative nature of the sQGP is evaluated within the Dynamical Quasi-Particle Model (DQPM) which is matched to reproduce the equation of state of the partonic matter above the deconfinement temperature $T_c$ from lattice QCD. The calculation of diffusion coefficients is based on two methods: i) the Chapman-Enskog method for the linearized Boltzmann equation, which allows to explore non-equilibrium corrections for the phase-space distribution function in leading order of the Knudsen numbers as well as ii) the relaxation time approximation (RTA). In this work we explore the differences between the two methods. We find a good agreement with the available lattice QCD data in case of the electric charge diffusion coefficient (or electric conductivity) at vanishing baryon chemical potential as well as a qualitative agreement with the recent predictions from the holographic approach for all diagonal components of the diffusion coefficient matrix. The knowledge of the diffusion coefficient matrix is also of special interest for more accurate hydrodynamic simulations.

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arXiv2019

Transport coefficients for the hot quark-gluon plasma at finite chemical potential $μ_B$

We calculate transport coefficients of the quark-gluon plasma (QGP) within the dynamical quasiparticle model (DQPM) by explicitly computing the parton interaction rates as a function of temperature $T$ and baryon chemical potential $μ_B$ on the basis of the DQPM couplings and partonic propagators. The latter are extracted from lattice QCD by matching the equation of state, entropy density and energy density at $μ_B$= 0. For baryon chemical potentials $0 \leq μ_B \leq 500 MeV$ we employ a scaling Ansatz for the effective coupling which was shown before to lead to thermodynamic consistent results in this range. We compute the ratio of the shear and bulk viscosities to the entropy density, i.e. $η/s$ and $ζ/s$, the electric conductivity $σ_0/T$ as well as the baryon diffusion coefficient $κ_B$ and compare to related approaches from the literature. We find that the ratios $η/s$ and $ζ/s$ as well as $σ_0/T$ are in accord with the results from lattice QCD at $μ_B$=0 and only weakly depend on the ratio $T/T_c(μ_B)$ where $T_c(μ_B)$ denotes the critical temperature at finite baryon chemical potential.

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arXiv2019

Exploring the partonic phase at finite chemical potential within an extended off-shell transport approach

We extend the Parton-Hadron-String Dynamics (PHSD) transport approach in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections as a function of temperature $T$ and baryon chemical potential $μ_B$ on the basis of the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. The ratio of shear viscosity $η$ over entropy density $s$, i.e. $η/s$, is evaluated using the collisional widths and compared to lQCD calculations for $μ_B$ = 0 as well. We find only a very modest change of $η/s$ with the baryon chemical $μ_B$. This also holds for a variety of hadronic observables from central A+A and C+Au collisions in the energy range 5 GeV $\leq \sqrt{s_{NN}} \leq$ 200 GeV when implementing the differential cross sections into the PHSD approach. We only observe small differences in the strangeness and antibaryon sector with practically no sensitivity of rapidity and $p_T$ distributions to the $μ_B$ dependence of the partonic cross sections. Since we find only small traces of a $μ_B$-dependence in heavy-ion observables - although the effective partonic masses and widths as well as their partonic cross sections clearly depend on $μ_B$ - this implies that one needs a sizable partonic density and large space-time QGP volume to explore the dynamics in the partonic phase. These conditions are only fulfilled at high bombarding energies where $μ_B$ is, however, rather low. On the other hand, when decreasing the bombarding energy and thus increasing $μ_B$, the hadronic phase becomes dominant and accordingly, it will be difficult to extract signals from the partonic dynamics based on "bulk" observables.

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